Stitch-forming mechanisms for sewing machines



1, .1967 M. WIENER ET AL 3,333,560

STITCHFORMING MECHANISMS FOR SEWING MACHINES 5 Sheets-Sheet 1 Filed Oct. 5, 1965 n. f e M Y 0 1 m w m W J n w W r W T e 4! A l GM of W W Y 8 2 .m F

WITNESS fi/ laaw 941 g- 1, 1957 M..WIENER ET AL 3,333,560

STITCH-FORMING MECHANISMS FOR SEWING MACHINES 3 Sheets-Sheet 2 Filed Oct. 5, 1965 'Illlllllll Fig.5

INVENTORS Walter J. Clifton Melvin Wiener B @LL ATTORNEY WI TNESS Www Aug. 1, 1967 W|ENER ET AL 3,333,560

STITCH-FORMING MECHANISMS FOR SBWING MACHINES s sheets-sheet;

Filed Oct. 5, 1965 INVENTORS Walter J. C/i'f fon Melvin Wiener ATTORNEY United States Patent 3,333,560 STITCH-FORMING NIECHANISMS FOR SEWING MACHINES Melvin Wiener, Rockaway, and Walter J. Clifton, Ridgewood, NJ., assignors to The Singer Company, New

York, N.Y., a corporation of New Jersey Filed Oct. 5, 1965, Ser. No. 493,211 14 Claims. (Cl. 112-199) This invention relates to stitch-forming mechanisms for sewing machines and more particularly to a pneumatic two-motion under-thread looper mechanism for forming a two-thread chain stitch in cooperation with an endwise reciprocating needle carrying an upper thread.

It is common in conventional two-thread chain stitch sewing machines to employ a four-motion looper in the work-supporting bed carrying thread from a supply of under thread. In order to impart to the looper its characteristic four motions of loop-seizing and shedding :as well as needle-avoiding it is necessary to provide a complicated mechanism requiring meticulous coordination of parts. Moreover, the looper mechanism is a major source of machine vibration, and is not an optimum mechanism for high speed operation. Where two motion loopers, i.e., loopers without needle-avoiding motion, have been used heretofore, loop spreader mechanisms have been required which frequently involve greater mechanical complexity than the mechanism for imparting needle-avoiding motion to the looper.

It is, therefore, a primary object of this invention to provide a pneumatic under-thread stitch-forming mechanism which does not require a needle-avoid mechanism or a loop spreader mechanism.

Another object of the invention is to provide a looper mechanism of increased stability and especially adapted for high speed operation in accordance with the foregoing object.

Another object of the invention is to provide a pneumatic under-thread stitch-forming mechanism which does not require a needle-avoid mechanism and which is capable of forming a two-thread chain stitch during reverse feeding as well as during forward feeding,

The objects of the invention are accomplished by providing a two-motion looper with a pneumatic loop-forming means. A thread-carrying conduit is formed inside the looper with an orifice at the eye of the looper. A second conduit communicates with the thread-carrying conduit and is connected to a source of compressed air. The inlet of the thread-carrying conduit has a reduced cross-sectional area in order to minimize backfiow of air through the inlet. Formed on the looper is a bulge to hold a loop of thread from the needle. On the loop-shedding stroke of the looper, the looper thread is blown out into a loop for penetration by the needle, thus obviating the need for any looper needle-avoid motion.

In order to accomplish reverse feeding, an external conduit may be provided in the frame. The external conduit is connected to a source of compressed air and is aimed toward the front of the looper to properly expand the looper-thread loop during reverse feeding for penetration by the needle. Alternatively, the air pressure through the conduit in the looper may be reduced to cause the looper-thread loop to change its position for penetration by the needle dun'ng'reverse feeding,

Other objects and a fuller understanding of the invention may be had by referring to the following description and claims, taken in conjunction with the accompanying drawings in which:

FIG. 1 is a top perspective view of a pneumatic looper mechanism in place in a work-supporting bed of a sewing machine; a

3,333,560 Patented Aug. 1, 1967 FIG. 2 is a substantially horizontal cross-sectional view as viewed from the top of the looper taken through conduits for thread and compressed air inside the looper;

FIG. 3 is a perspective view of the needle and the looper beginning to form a two-thread chain stitch with a portion of the work-supporting bed in section and with the needle beginning its upstroke and the looper beginning its loop-seizing stroke;

FIG. 4 is a perspective view as in FIG. 3 with the looper beginning its loop-shedding stroke and the needle beginning its loop-penetrating stroke;

FIG. 5 is a perspective view as in FIG. 3 with the needle at the bottom of its downstroke and the looper ready to begin another loop-seizing stroke;

FIG. 6 is a top plan view of the looper blade showing the needle penetrating the looper-thread loop during forward feeding;

FIG. 7 is a substantially horizontal cross-sectional view of the looper blade of FIG. 6 as viewed from the top of the blade showing why the needle cannot penetrate the looper-thread loop during reverse feeding;

FIG. 8 is a substantially horizontal cross-sectional view of the looper as viewed from the top of the blade showing schematically a first modification of the invention which permits reverse feeding;

FIG. 9 is a substantially horizontal cross-sectional view of a looper blade as viewed from the top of the blade showing a second modification of the invention during forward feeding; and

FIG. 10 is a substantially horizontal cross-sectional schematic view of the looper of FIG. 9 as viewed from the top of the looper showing the looper during reverse feeding.

With reference to the drawings, the invention is illustrated as embodied in a two-thread chain stitch machine having a frame of which only a portion of a worksupporting bed 10 is shown. A throat plate 11 is mounted on the bed, and the bed has an opening 12 for a slide plate (not shown).

Mounted in the bed is work feeding mechanism represented by a feed dog 13. The fed :dog is opposed by a presser foot 14 which is mounted on the frame in a conventional manner.

Also mounted on the frame is a needle 15 which is connected to a needle bar 16 by a setscrew 17. Endwise reciprocation is imparted to the needle through the needle bar in a conventional manner. The needle reciprocates through a needle aperture 18 in the throat plate 11 and has an eye 19 to carry thread 20 from a supply of upper thread.

A stitch-forming means represented by a two-motion looper, indicated generally at 21, is mounted in the bed. Loop-seizing and loop-shedding motions are imparted to the looper by a conventional mechanism of which only a portion of a looper bar 22 is shown. The looper is secured to the looper bar by screws 23.

The looper 21 has a blade 24 and a nose portion 25 at the end of the blade with an eye 26 formed therein. A thread-carrying conduit 27 is formed in the blade with an inlet portion 28 for thread, an intermediate portion 29, and an orifice portion 30 communicating with the eye 26 of the looper. The orifice portion of the conduit is formed at an obtuse angle with respect to the intermediate portion of the conduit and forms approximately a 45 degree angle with the plane of the eye of the looper.

The thread-carrying conduit 27 carries thread 31 from a supply of under thread. The thread from the supply of under thread passes through a looper-thread take-up mechanism, indicated generally at 32, which may be of the type disclosed in a United States patent of A. B. Clayton, No, 2,095,212, granted Oct. 5, 1937.

A pneumatic means represented by a second conduit 33 is formed in the looper 21 and communicates with the thread-carrying conduit 27. The second conduit has an inlet portion 34 to which a plastic air hose 35 is connected. The air hose is in turn connected to a source of compressed air (not shown). In order to minimize backflow of air through the inlet portion 28 of the threadcarrying conduit 27, a bushing 36 is inserted in the inlet portion .28 to reduce the cross-sectional area.

Formed on the blade 24 of the looper is a bulge 37. The bulge assists in delaying the shedding of a loop of needle thread from the looper on its loop-shedding stroke.

In operation, air with 30 pounds per square inch pressure is continuously introduced into the thread-carrying conduit 27 of the looper 21 by means of the pneumatic conduit 33 and the air hose 35 which is connected to the inlet portion 34 of the pneumatic conduit.

With specific reference to FIGS. 3 to 5, the looper 21 and the needle 15 are shown in three different positions during the formation of a single two-thread chain stitch S1.

Beginning with FIG. 3 as the needle 15 begins its upstroke, a loop 38 of thread is formed on one side of the needle because of the actions of a conventional needlethread take-up mechanism -(not shown) in providing slack thread and friction imposed on a portion of the needle' thread which is wedged between the needle and a side penetration 39 in the work material. But, the immediately preceding needle penetration is on the eye-side of the looper blade and the looper thread is blown out into a loop 41 between, the orifice portion 30 of the conduit 27 and the needle penetration 39 which is too shallow for penetration by the needle because of the position of the immediately preceding needle penetration 39 in the work material 40.

With specific reference to FIG. 8, a first modification of the invention is shown which is capable of forming a two-thread chain stitch during reverse feeding, or during back-tacking to secure the stitches at the end of a seam.

In order to properly expand the loop 41 of looper thread for penetration by the needle during reverse feeding, a first modification of the invention may be provided. As shown in FIG. 8, an external conduit 45 is positioned in the Work-supporting bed 10. The conduit has a pinholesize orifice 46 which is aimed toward the front of the looper 21 to expand the loop 41 of looper thread by directing an auxiliary stream of air' at the loop 41. A

valve 48 is connected to the conduit 45 to be opened during reverse feeding by the controlmeans or regulator lever 48 for the feed mechanism. The conduit 45 is com nected to the source of compressed air (not shown).

of a penetration 39 produced by the needle in an article illustrated. i Moving on to FIG. 4, the looper 21 seizes the loop 38 of needle thread and holds it behind the bulge 37 on the looperblade 24 during the first part of the loop-shedding stroke. As the looper moves away from the needle 15 in its loop-shedding stroke,- the looper-thread take-up mechanism .32 provides slack thread and the compressed air which is continuously introduced into the threadcarrying conduit 27 blows a loop 41 of looper thread out of-the looper eye 26 into substantially a horizontal plane for penetration by the needle which has gone all the way to the top of its upstroke and has penetrated the work material 40 again on a downstroke. An end of the looper loop 41 is held by the work material 40, and the feed dog- 13 has fed the work material one stitch length.

.- In FIG. 5, the needle loop 38 has been shed from the bulge 37 on the blade 24 of the looper 21 on the loopshedding stroke and has been pulled up into the work material 40 by the action of the needle-thread take-up mechanism (not shown) to complete the stitch S1. The looper-thread take-up mechanism 32 has pulled the looper loop 41 taut around the needle 15 for a second stitch S2 which is how .thecorresponding looper loop 43 of the stitch S1 was set, and the needle is about to begin a second up-stroke to form another loop 44 of needle thread for penetration by the looper as in FIG. 3 to form the second stitch S2.

In FIG. 6, a top plan view of the looper blade 24 is shown during forward feeding. The loop 38 of needle thread-is held on the looper blade andboth limbs of thread extend into the immediately preceding needle penetration 39 for the stitch S1 in the work material 40. The looper thread'is blown out into a loop 41 between the orifice portion of the conduit 27 and the needle penetration-39. Since the orifice portion is at approximately a 45 degree angle with respect to the plane of the eye 26 of the looper, the loop 410i looper thread With specific reference to FIGS. 9 and 10, a second modification of the invention is shown for forming a twothread chain stitch during reverse feeding.

In the second modification, the orifice portion 49 of the conduit 27 is formed at approximately a right angle with respect to the intermediate portion 29 of the conduit, and a thread-size slot 50 is formed in the looper blade 24 extending forwardly from the orifice portion 49 of the conduit. A valve 51 is connected to the second conduit 33 which supplies compressed air to the thread-carrying conduit 27. The valve 51 is operated by the regulator lever 48 for the feed mechanism. j

During forward feeding, as shown in FIG. 9, the regular air pressure blows the loop 41 of looper thread out into a normal loop between the. orifice portion'49 of the conduit 27 and the immediately preceding needle penetration 39 in the work material 40. The loop 41 of looper thread does not extend into the slot 50 in the looper blade 24 because it is entrained in the blast of air out; the orifice portion 49 of the looper blade.

As shown in FIG. 10, during reverse feeding, the air" of the looper thread.

Although the invention has been described in its preferred form with a certain degree of particularity, it is understood that the present disclosure of the preferred form has been made by way of example and that numerous changes in the details of construction and the combination and arrangement of parts maybe resorted to without 'departing from the spirit and the scope of the invention.

Having thus described the nature of the invention, what is claimed herein is:

1. A pneumatic under-thread stitch-forming mechanism for a chain stitch sewing machine having a frame, a feed mechanism mounted in the frame, a supply of upper thread associated with the frame, an endwise reciprocating needle mounted on the frame to carry thread from said upper-thread supply, and a supply of under thread associated with the frame, said pneumatic stitchforming mechanism comprising stitch-forming means mounted in the frame to carry thread from said underthread supply, pneumatic means for cylically forming a' loop of under thread on the stitch-forming means for penetration by the needle, and a mechanism for, imparting loop-seizing and loop-shedding motions to said stitch forming means in timed relation with the needle in the penetration of under-thread loops formed on the stitchforming means by said pneumatic means and in cooperation with the feed mechanism to form a two-thread chain stitch.

2. A pneumatic under-thread stitch-forming mechanism for a chain stitch sewing machine having a frame, a mechanism mounted in the frame, a supply of upper thread associated with the frame, an endwise reciprocating needle mounted on the frame to carry thread from said upper-thread supply, and a supply of under thread associated with the frame, said pneumatic stitch-forming mechanism comprising stitch-forming means mounted in the frame and having an eye and a conduit communicating with the eye to carry thread from said under-thread supply, pneumatic means communicating with said conduit for cyclically forming a loop of under-thread through the eye of the stitch-forming means for penetration by the needle, and a mechanism for imparting loop-seizing and loop-shedding motions to said stitch-forming means in timed relation with the needle in the penetration of underthread loops formed through the eye of the stitch-forming means by said pneumatic means and in cooperation with the feed mechanism to form a two-thread chain stitch.

3. A pneumatic under-thread stitch-forming mechanism for a chain stitch sewing machine having a frame, a feed mechanism mounted in the frame, a supply of upper thread associated with the frame, an endwise reciprocating needle mounted on the frame to carry thread from said upper thread supply, a supply of under thread associated with the frame, and a take-up mechanism for the under thread mounted on the frame, said pneumatic stitchforming mechanism comprising stitch-forming means mounted in the frame and having an eye and a conduit communicating with the eye to carry thread from said under-thread supply, said conduit having an inlet with a reduced cross sectional area at the end opposite from the eye, pneumatic means communicating with said conduit between the inlet and the eye for cyclically forming a loop of under thread through the eye of the stitch-forming means in cooperation with said take-up mechanism for penetration by the needle, and a mechanism for imparting loop-seizing and loop-shedding motions to said stitch-forming means in timed relation with the needle in the penetration of under-thread loops formed through the eye of the stitch-forming means by said pneumatic means and said take-up mechanism and in cooperation with the feed mechanism to form a two-thread chain stitch.

4. A pneumatic two-motion under-thread stitch-forming mechanism for a chain stitch sewing machine having a frame, a feed mechanism mounted in the frame, a supply of upper thread associated with the frame, an endwise reciprocating needle mounted on the frame to carry thread from said upper thread supply, a supply of under thread associated with the frame, and a take-up mechanism for the under thread mounted on the frame, said pneumatic stitch-forming mechanism comprising stitchforming means mounted in the frame and having an eye and a conduit communicating with the eye to carry thread from said under-thread supply, said conduit having an inlet with a reduced cross sectional area at the end opposite from the eye and having the eye-end formed at an obtuse angle with respect to the intermediate portion of the conduit, pneumatic means communicating with said conduit between the inlet and the eye for cyclically forming a loop of under thread through the eye of the stitchforming means in cooperation with said take-up mechanism for penetration by the needle 'by directing continuous stream of air through said conduit, and a mechanism for imparting loop-seizing and loop-shedding motions to said stitch-forming means in timed relation with the needle in the penetration of under-thread loops formed through the eye of the stitch-forming means by said pneumatic means and said take-up mechanism and in cooperation with the feed mechanism to form a two-thread chain stitch.

5. The stitch-forming mechanism of claim 4, in which the eye-end of said conduit forms an angle of approximately 45 degrees with respect to the plane of the portion of said stitch-forming means in which the eye is formed.

6. A pneumatic under-thread looper mechanism for a chain stitch sewing machine having a frame, a feed mechanism mounted in the frame, a supply of upper thread associated with the frame, an endwise reciprocating needle mounted on the frame to carry thread from said upper-thread supply, and a supply of under thread associated with the frame, said pneumatic looper mechanism comprising a looper mounted in the frame to carry thread from said under-thread supply, pneumatic means for cyclically forming a loop of under thread on the looper for penetration by the needle, a loop-holding bulge on the looper, and a mechanism for imparting loop-seizing and loop-shedding motions to the looper in timed relation with the needle in the penetration of under-thread loops formed on the looper by said pneumatic means and in cooperation with the feed mechanism to form a twothread chain stitch.

7. A pneumatic under-thread looper mechanism for a chain stitch sewing machine having a frame, a feed mechanism mounted in the frame, a supply of upper thread associated with the frame, an endwise reciprocating needle mounted on the frame to carry thread from said upper-thread supply, and a supply of under thread associated with the frame, said pneumatic looper mechanism comprising a looper mounted in the frame and having an eye and a conduit communicating with the eye to carry thread from said under-thread supply, pneumatic means communicating with said conduit for cyclically forming a loop of under thread through the eye of the looper for penetration by the needle, 2. loop-holding bulge on the looper, and a mechanism for imparting loopseizing and loop-shedding motions to the looper in timed relation with the needle in the penetration of under-thread loops formed through the eye of the looper by said pneumatic means and in cooperation with the feed mechanism to form a two-thread chain stitch.

8. A pneumatic under-thread looper mechanism for a chain stitch sewing machine having a frame, a feed mechanism mounted in the frame, a supply of upper thread associated with the frame, an endwise reciprocating needle mounted on the frame to carry thread from said upper thread supply, a supply of under thread associated with the frame, and a take-up mechanism for the under thread mounted on the frame, said pneumatic looper mechanism comprising a looper mounted in the frame and having an eye and a conduit communicating with the eye to carry thread from said under-thread supply, said conduit having an inlet with a reduced cross sectional area at the end opposite from the eye, pneumatic means communicating with said conduit between the inlet and the eye for cyclically forming a loop of under thread through the eye of the looper in cooperation with said take-up mechanism for penetration by the needle, a. loop-holding bulge on the looper, and a mechanism for imparting loop-seizing and loop-shedding motions to the looper in timed relation with the needle in the penetration of under-thread loops formed through the eye of the looper by said pneumatic means and said take-up mechanism and in cooperation with the feed mechanism to form a two-thread chain stitch.

9. A pneumatic two-motion under-thread looper mechanism for a chain stitch sewing machine having a frame, a feed mechanism mounted in the frame, a supply of upper thread associated with the frame, an endwise reciprocating needle mounted on the frame to carry thread from said upper thread supply, a supply of under thread associated with the frame, and a take-up mechanism for the under thread mounted on the frame, said pneumatic looper mechanism comprising a looper mounted in the frame and having an eye and a conduit communicating with the eye to carry thread from said under-thread supply, said conduit having an inlet with a reduced cross sectional area at the end opposite from the eye and having the eye-end formed at an obtuse angle with respect to the intermediate portion of the conduit, pneumatic means communicating with said conduit between the inlet and the eye for cyclically forming a loop of under thread through the eye of the looper in cooperation with said takeup mechanism for penetration by the needle by directing a continuous stream of air through said conduit, a loopholding bulge on the looper, and a mechanism for imparting loop-seizing and loop-shedding motions to the looper in timed relation with the needle in the penetration of under-thread loops formed through the eye of the looper by said pneumatic means and said take-up mechanism and in cooperation with the feed mechanism to form atwothread chain stitch.

10. The looper mechanism of claim 9 in which the eyeend of said conduit forms an angle of approximately 45 degrees with respect to the plane of the portion of said looper in which the eye is formed.

11. A pneumatic under-thread stitch-forming mechanism for a chain stitch sewing machine having a frame, a reverse feed mechanism mounted in the frame, control means connected to the feed mechanism, a supply of upper thread associated with the frame, an endwise reciprocating needle mounted on the frame to carry thread from said upper-thread supply, and a supply of under thread as sociated with the frame, said pneumatic stitch-forming mechanism comprising stitch-forming means mounted in t the frame and having an eye and a conduit communicating with the eye to carry thread from said under-thread supply, pneumatic means communicating with said conduit for cyclically forming a loop of under thread through the eye of the stitch-forming means for penetration by the needle, a mechanism for imparting loop-seizing and loop shedding motions to said stitch-forming means in timed relation with the needle in the penetration of underthread loops formed through the eye of the stitch-forming means by said pneumatic means and in cooperation with the feed mechanism to form a two-thread chain stitch, an external conduit in said frame aimed substantially toward the front of the looper on the eye-side of the looper to assist in expanding said loop of under thread for penetration by the needle during reverse feeding, and second pneumatic means for introducing air int-o said external conduit.

12. A pneumatic two-motion under-thread stitch-forming mechanism for a chain stitch sewing machine having a frame, a reverse feed mechanism mounted in the frame, control means connected to the feed mechanism, a supply of upper thread associated with the frame, an endwise reciprocating needle mounted on the frame to carry thread from said upper-thread supply, and a supply of under thread associated with the frame, said pneumatic stitch forming mechanism comprising stitch-forming means mounted in the frame and having an eye and a conduit communicating with the eyeto carry thread from said under-thread supply, said conduit having the eye-end formed at an obtuse angle with respect to the intermediate portion of the conduit, pneumatic means communicating with said conduit for cyclically forming a loop of under thread through the eye of the stitch-forming means for penetration by the needle, a mechanism for imparting lo opseizing and loop-shedding motions to said stitch-forming means in timed relation with the needle in the penetration of under-thread loops formed through the eye of the stitchforming means by said pneumatic means and in cooperation with the feed mechanism to form a two-thread chain stitch, an external conduit in said frame aimed substantially toward the front of the looper on the eye-side of the looper to assist in expanding said loop of under thread for penetration by the needle during reverse feeding, second pneumatic means for introducing air into said external conduit, and a valve on said second pneumatic means and connected to said control means for the feed mechanism to allow air to flow through said external conduit during reverse feeding.

13. A pneumatic under-thread stitch-forming mechanism for a chain stitch sewing machine having a frame, a reverse feed mechanism mounted in the frame, control means connected to the feed mechainsm, a supply of upper thread associated with the frame, an endwise reciprocating needle mounted on the frame to carry thread from said upper-thread supply, and a supply of under thread associated with the frame said pneumatic stitch-forming mechanism comprising stitch-forming means mounted in the frame and having an eye and a conduit communicating with the eye to carry thread from said under-thread supply, pneumatic means communicating with said conduit for cyclically forming a loop of under thread through the eye of the stitch-forming means for penetration by the needle, a mechanism for imparting loop-seizing and loopshedding motions to said stitch-forming means in timed relation wit-h the needle in the penetration of under-thread loops formed through the eye of the stitch-forming meansby said pneumatic means and in cooperation with the feed mechanism to form a two-thread chain stitch, and a valve on said pneumatic means and connected to said control means for the feed mechanism to change the air pressure in said conduit in the stitch-forming means during reverse feeding and hence the position of the loop of under thread so that the needle will penetrate the loop of under thread during reverse feeding.

14. A pneumatic under-thread looper mechanism for a chain stitch sewing machine having a frame, a reverse feed mechainsm mounted in the frame, control means connected to the feed mechanism, a supply of upper thread associated with the frame, an endwise reciprocating needle mounted on the frame to carry thread from said upperthread supply, and a supply of under thread associated with the frame, said pneumatic looper mechanism comprising a looper mounted in the frame and havingan eye and'a conduit communicating with the eye to carry thread from said under-thread supply, said conduit having the eyeend for-med at substantially a right angle with respect to the intermediate portion of the conduit and a substantially horizontal thread-size slot extending forwardly from the eye-end of the conduit, pneumatic means communicating with said conduit for cyclically forming a loop of underthread through the eye of the looper for penetration by the needle, a mechanism for imparting loop-seizing and loop-shedding motions to the looper in timed relation with the needle in the penetration of under-thread loops formed through the eye of the looper by said pneumatic means and in cooperation with the feed mechanism to form a twothread chain stitch, and a valve on said pneumatic means and connected to said control means for the feed mechanism to reduce the air pressure in said conduit in the looper during reverse feeding so that the loop of underthread will extend into said slot in the looper to change the position of the loop of under-thread during reverse feeding for penetration by the needle.

References Cited UNITED STATES PATENTS 50,117 9/1865 Hale 112-+-154 X 2,422,126 6/ 1947 Parker 11279 2,599,226 6/1952 Briem 112-79 2,812,735 11/1957 Nelson 112199 3,263,631 8/1966 Freeman l1279 FOREIGN PATENTS 1,106,948 7/ 1955 France.

JORDAN FRANKLIN, Primary Examiner. H. F. ROSS, Assistant Examiner. 

1. A PNEUMATIC UNDER-THREAD STITCH-FORMING MECHANISM FOR A CHAIN STITCH SEWING MACHINE HAVING A FRAME, A FEED MECHANISM MOUNTED IN THE FRAME, A SUPPLY OF UPPER THREAD ASSOCIATED WITH THE FRAME, AN ENDWISE RECIPROCATING NEEDLE MOUNTED ON THE FRAME TO CARRY THREAD FROM SAID UPPER-THREAD SUPPLY, AND A SUPPLY OF UNDER THREAD ASSOCIATED WITH THE FRAME, SAID PNEUMATIC STITCHFORMING MECHANISM COMPRISING STITCH-FORMING MEANS MOUNTED IN THE FRAME TO CARRY THREAD FROM SAID UNDERTHREAD SUPPLY, PNEUMATIC MEANS FOR CYCLICALLY FORMING A LOOP OF UNDER THREAD ON THE STITCH-FORMING MEANS FOR PENETRATION BY THE NEEDLE, AND A MECHANISM FOR IMPARTING LOOP-SEIZING AND LOOP-SHEDDING MOTIONS TO SAID STITCHFORMING MEANS IN TIMED RELATION WITH THE NEEDLE IN THE PENETRATION OF UNDER-THREAD LOOPS FORMED ON THE STITCHFORMING MEANS BY SAID PNEUMATIC MEANS AND IN COOPERATION WITH THE FEED MECHANISM TO FORM A TWO-THREAD CHAIN STITCH. 